U.S. patent number 8,188,304 [Application Number 11/689,719] was granted by the patent office on 2012-05-29 for process for the purification of lanthanide carboxylates.
This patent grant is currently assigned to Polimeri Europa S.p.A.. Invention is credited to Paolo Biagini, Lucia Bonoldi, Franco Cambisi, Liliana Gila, Mario Salvalaggio.
United States Patent |
8,188,304 |
Biagini , et al. |
May 29, 2012 |
**Please see images for:
( Certificate of Correction ) ** |
Process for the purification of lanthanide carboxylates
Abstract
A process is described for the purification of lanthanide
carboxylates which comprises a step in which the hydrocarbon
solution deriving from the synthesis of lanthanide carboxylate,
containing said carboxylate and impurities of the corresponding
carboxylic acid and/or water, is treated with an aqueous solution
of a base in order to obtain a pH of the aqueous phase ranging from
9.0 to 12.2 and/or a step in which the hydrocarbon solution
containing lanthanide carboxylate is treated with a solid selected
from Na.sub.2SO.sub.4, MgSO.sub.4, Mg(ClO.sub.4).sub.2, molecular
sieves 3 .ANG., molecular sieves 4 .ANG., molecular sieves 5 .ANG.
and molecular sieves 13 X. Analytical methods are also described,
which allow the purity of the lanthanide carboxylates to be
non-destructively measured.
Inventors: |
Biagini; Paolo (Trecate,
IT), Salvalaggio; Mario (Moriondo Torinese,
IT), Cambisi; Franco (Oleggio, IT),
Bonoldi; Lucia (Milan, IT), Gila; Liliana
(Casalino, IL) |
Assignee: |
Polimeri Europa S.p.A.
(Brindisi, IT)
|
Family
ID: |
37075893 |
Appl.
No.: |
11/689,719 |
Filed: |
March 22, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070232794 A1 |
Oct 4, 2007 |
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Foreign Application Priority Data
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Mar 31, 2006 [IT] |
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MI06A0619 |
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Current U.S.
Class: |
554/71; 562/490;
562/606 |
Current CPC
Class: |
C07C
51/47 (20130101); C08F 36/04 (20130101); C07C
51/48 (20130101); C07C 51/47 (20130101); C07C
53/126 (20130101); C07C 51/47 (20130101); C07C
53/128 (20130101); C07C 51/47 (20130101); C07C
63/36 (20130101); C07C 51/48 (20130101); C07C
53/126 (20130101); C07C 51/48 (20130101); C07C
53/128 (20130101); C07C 51/48 (20130101); C07C
63/36 (20130101); C08F 36/04 (20130101); C08F
4/545 (20130101); G01N 21/3577 (20130101); G01N
21/3563 (20130101) |
Current International
Class: |
C07F
13/00 (20060101); C07C 63/36 (20060101); C07C
53/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 564 081 |
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Oct 1993 |
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EP |
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WO 97/36850 |
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Oct 1997 |
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WO |
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WO 98/39283 |
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Sep 1998 |
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WO |
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WO 99/54335 |
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Oct 1999 |
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WO |
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Other References
Armarego et al, Purification of Laboratory Chemicals, 4th Edition,
2000, pp. 1-47. cited by examiner.
|
Primary Examiner: Zucker; Paul A
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
The invention claimed is:
1. A process for purifying a hydrocarbon solution deriving from the
synthesis of a lanthanide carboxylate, comprising said lanthanide
carboxylate and impurities of the corresponding carboxylic acid
and/or water, comprising: treating the hydrocarbon solution,
comprising lanthanide carboxylate, with an aqueous solution of a
base to obtain a pH of the aqueous phase ranging from 11.0 to 11.8;
and optionally treating the hydrocarbon solution comprising
lanthanide carboxylate with a solid selected from the group
consisting of Na.sub.2SO.sub.4, MgSO.sub.4, Mg(ClO.sub.4).sub.2,
molecular sieves 3 .ANG., molecular sieves 4 .ANG., molecular
sieves 5 .ANG. and molecular sieves 13 X.
2. The process according to claim 1, comprising: treating the
hydrocarbon solution, comprising lanthanide carboxylate, with an
aqueous solution of a base to obtain a second hydrocarbon solution
with a pH of the aqueous phase ranging from 11.0 to 11.8; and
treating the second hydrocarbon solution comprising lanthanide
carboxylate with a solid selected from the group consisting of
Na.sub.2SO.sub.4, MgSO.sub.4, Mg(ClO.sub.4).sub.2, molecular sieves
3 .ANG., molecular sieves 4 .ANG., molecular sieves 5 .ANG. and
molecular sieves 13 X.
3. The process according to claim 1, wherein the solution of the
base has a concentration ranging from 0.01 to 2 M.
4. The process according to claim 1, wherein the carboxylic acid is
a mono-carboxylic acid or polycarboxylic acid comprising from 2 to
40 carbon atoms selected from the group consisting of aliphatic
acid, cyclo-aliphatic acid, alicyclic acid and aromatic acid.
5. The process according to claim 4, wherein the acid comprises
from 6 to 20 carbon atoms.
6. The process according to claim 5, wherein the acid comprises
from 8 to 12 carbon atoms.
7. The process according to claim 6, wherein the acid is versatic
acid, naphthenic acid or 2-ethyl hexanoic acid.
8. The process according to claim 1, wherein the solution of
lanthanide carboxylate is a solution of neodymium, praseodymium,
gadolinium, lanthanum carboxylate, or mixtures thereof.
9. The process according to claim 1, wherein the lanthanide
carboxylate is selected from the group consisting of neodymium
versatate, neodymium naphthenate and neodymium
2-ethyl-hexanoate.
10. The process according to claim 1, wherein the base is selected
from the group consisting of a hydroxide of an alkaline earth
metal, an oxide of alkaline earth metal, a hydroxide of alkaline
earth metal, an oxide of alkaline earth metal, ammonia and an
organic amine.
11. The process according to claim 10, wherein the base is sodium
hydroxide or potassium hydroxide.
12. The process according to claim 2, wherein the solid comprises
molecular sieves 3 .ANG..
13. The process according to claim 2, wherein in said treating the
hydrocarbon solution comprising lanthanide carboxylate with a
solid, the hydrocarbon solution is circulated in continuous, with a
pump, through a column filled with a solid selected from the group
consisting of Na.sub.2SO.sub.4, MgSO.sub.4, Mg(ClO.sub.4).sub.2,
molecular sieves 3 .ANG., molecular sieves 4 .ANG., molecular
sieves 5 .ANG. and molecular sieves 13X.
14. The process according to claim 1, wherein said treating the
hydrocarbon solution comprising lanthanide carboxylate with the
aqueous solution of a base is repeated.
15. The process according to claim 2, wherein said treating the
hydrocarbon solution comprising lanthanide carboxylate with the
aqueous solution of a base is repeated.
16. The process according to claim 2, wherein said treating the
hydrocarbon solution comprising lanthanide carboxylate with the
solid is repeated.
17. The process according to claim 2, wherein said treating the
hydrocarbon solution comprising lanthanide carboxylate with the
aqueous solution of a base is repeated, and said treating the
hydrocarbon solution comprising lanthanide carboxylate with the
solid is repeated.
18. The process according to claim 1, wherein the purified
hydrocarbon solution has a molar ratio of lanthanide to carboxylic
acid of greater than 100.
19. The process according to claim 2, wherein the purified
hydrocarbon solution has a molar ratio of lanthanide to carboxylic
acid of greater than 100.
20. The process according to claim 2, wherein the purified
hydrocarbon solution has a molar ratio of lanthanide to water of
greater than 60.
21. The process according to claim 2, wherein the purified
hydrocarbon solution has a molar ratio of lanthanide to carboxylic
acid of greater than 100, and wherein the purified hydrocarbon
solution has a molar ratio of lanthanide to water of greater than
60.
Description
A process is described for the purification of lanthanide
carboxylates which comprises a step in which the hydrocarbon
solution deriving from the synthesis of lanthanide carboxylate,
containing said carboxylate and impurities of the corresponding
carboxylic acid and/or water, is treated with an aqueous solution
of a base in order to obtain a suitable pH of the aqueous phase,
and/or a step in which the hydrocarbon solution containing
lanthanide carboxylate is treated with a solid selected from
Na.sub.2SO.sub.4, MgSO.sub.4, Mg(ClO.sub.4).sub.2, molecular sieves
3 .ANG., molecular sieves 4 .ANG., molecular sieves 5 .ANG. and
molecular sieves 13 X.
Analytical methods are also described, which allow the purity of
the lanthanide carboxylates to be non-destructively measured.
Polybutadiene with a high content of 1,4-cis units (>90%) is
produced industrially with the use of catalysts of the
Ziegler-Natta type, which consist of compounds of transition metals
or of the series of lanthanides in the presence of one or more
cocatalysts. Among these catalytic systems, those based on the use
of compounds of elements of the series of lanthanides, are
particular interesting as they have a wide range of conditions of
use, they provide polymers with an extremely high content of
1,4-cis units (>96%) and can operate in solvents completely free
of aromatic hydrocarbons.
In the presence of suitable activators, many derivatives of metals
of the series of lanthanides can generate valid catalytic systems
for the production of 1,4-cis polybutadiene, but among all of
these, those which have been most widely used are undoubtedly
carboxylates. The reasons lie in the fact that these compounds are
generally easy to synthesize starting from easily available and
low-cost precursors, furthermore they do not have to be kept in an
inert environment and, depending on the carboxylic acid used, they
are extremely soluble in aliphatic hydrocarbons, i.e. in the
solvents in which the polymerization process of butadiene generally
takes place.
Numerous synthesis methods of lanthanide (Ln) carboxylates provide
materials, solid or in solution, which contain, in addition to the
desired product Ln(OOCR).sub.3, varying quantities of the
corresponding carboxylic acid RCOOH and/or H.sub.2O. U.S. Pat. No.
5,783,676, for example, describes a method for obtaining solid
Nd(Vers).sub.3 by the reaction between Na(Vers) and
Nd(NO.sub.3).sub.3 using mixtures of methanol/water as solvent:
under these conditions, the products obtained contain up to 5% by
weight of free versatic acid and varying quantities of H.sub.2O, in
any case >0.1% by weight, in relation to the particular
experimental conditions adopted. Analogously U.S. Pat. No.
6,054,563 and U.S. Pat. No. 6,090,926 describe a method for
obtaining solid Nd(Vers).sub.3 starting from the corresponding
hydrocarbon solutions containing H.sub.2O (from 0.005 to 3% by
weight) and free versatic acid (from 0.005 to 12% by weight), in
some cases a series of solubilizing agents among which the same
carboxylic acids, are added to the solutions, before the drying
phase.
With respect to the production of hydrocarbon solutions containing
neodymium carboxylates, two main strategies are adopted. The first
consists in reacting Nd.sub.2O.sub.3 directly with the desired
carboxylic acid, mainly versatic acid or naphthenic acid, in the
presence of catalytic quantities of HCl, and varying quantities of
H.sub.2O and/or neodymium salts such as NdCl.sub.3 or
Nd(NO.sub.3).sub.3 are sometimes added, in order to facilitate the
reaction. Valid examples of this synthesis method are described in
U.S. Pat. No. 4,710,553, U.S. Pat. No. 5,686,371, EP 0,562,081, EP
0,968,992, U.S. Pat. No. 6,111,082 and U.S. Pat. No. 6,482,906. The
amount of H.sub.2O and carboxylic acid present in the final
solutions are not always mentioned in the examples considered, but
the available data suggest that, under these conditions, the molar
ratios H.sub.2O/Nd and carboxylic acid/Nd in the final hydrocarbon
solutions can vary from 0.2 to values higher than 1.5. In some
case, such as in EP 0.968.992 and U.S. Pat. No. 6,111,082, the
quantity of H.sub.2O is considerably reduced through an azeotropic
distillation, but in no case are described operations which intend
to eliminate or reduce the amount of free carboxylic acid present
in the Nd(Ver).sub.3 solutions.
A second strategy envisages a reaction between neodymium salts,
such as, for example, NdCl.sub.3 or Nd(NO.sub.3).sub.3, with sodium
carboxylates or carboxylic acids in the presence of amines, in
water as solvent. In this way, the corresponding neodymium
carboxylate is formed and can be subsequently extracted by means of
organic solvents as described in U.S. Pat. No. 4,520,177 and U.S.
Pat. No. 4,689,368, or the product is obtained directly in an
organic solution, if the reaction is effected in the presence of an
H.sub.2O/organic solvent double phase as exemplified in U.S. Pat.
No. 5,220,045, U.S. Pat. No. 6,111,082 and WO 02/076992. This
synthesis method also produces solutions of Nd(Vers).sub.3
containing variable amounts of free carboxylic acid and water. The
quantity of the latter is, in many cases, decreased through
azeotropic distillations, but nothing is done to decrease the
amount of free acid present in the solutions. On the contrary, as
declared in U.S. Pat. No. 6,111,082 and WO 02/076992, it is
necessary to add further amounts of solubilizing agents, among
which also the same carboxylic acids, to allow the hexane solutions
of Nd(Vers).sub.3, obtained with this method, to remain stable for
long periods of time.
The free carboxylic acid present in the solutions or in the solid
products based on Nd(Vers).sub.3, can derive from the use of an
excess of this reagent in the attack reaction of the corresponding
oxide, whereas water can be present both because it is used as
solvent, for example in reactions between salts of lanthanides and
sodium carboxylates, and also because it is produced in the
reactions between lanthanide oxides (Ln.sub.2O.sub.3) and
carboxylic acids. In some cases, as mentioned above, the addition
of variable quantities of carboxylic acid is described with the
purpose of improving the stability of the hydrocarbon solutions of
lanthanide carboxylates.
The presence of variable and non-reproducible amounts of carboxylic
acid and/or water in the solutions containing lanthanide
carboxylates can cause considerable drawbacks during the activation
phase, before polymerization, which normally includes the use of
alkylating agents, such as, for example, aluminum alkyls. As it is
known to experts in the field, the presence of substances
containing acidic hydrogens, as in the case of carboxylic acids and
water, causes an immediate hydrogenolysis reaction of the
alkylating reagent with the formation of the corresponding
carboxylates or oxides. From this it follows that, in the
formulation of the catalytic system, a higher quantity of
alkylating reagent must be used and, as these products normally
have a high cost with respect to the other components, this
operation considerably increases the relative costs of the
catalytic system.
Furthermore, when derivatives based on aluminum are used as
alkylating agents, the relative products of partial hydrogenolysis
which are obtained by reaction with carboxylic acids and water,
consist of dialkyl aluminum carboxylates and alumoxanes,
respectively; these products are normally soluble in hydrocarbon
solvents and therefore can react with the catalytic system and
modify its characteristics, both by causing a decrease in the
polymerization kinetics and by modifying the profile of the
molecular weight distribution of the polybutadiene produced.
It is therefore evident that it would be desirable to avail of a
method which allows the production of solutions of carboxylates of
lanthanides with no carboxylic acid or water at all, or the lowest
possible amount thereof, in order to optimize the aluminum
consumption and maintain constant the characteristics of the
polybutadiene produced, and it would also be useful to have a
simple, rapid and non-destructive analytical method and easy to
use, in order to directly determine the residual amount of
carboxylic acid and water, or possibly the sum of the two products,
in these solutions.
A method has now been found by the Applicant, for regulating the
quantity of carboxylic acid and water present in hydrocarbon
solutions of lanthanide carboxylate, until complete
elimination.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1. The IR spectrum of a cyclohexanic solution of pure
Nd(Vers).sub.3 (dotted line) and the IR spectrum obtained after the
addition, to the same solution, of versatic acid (broken line,
Nd(Vers).sub.3/VersH molar ratio 1:1.47.
FIG. 2a. A calibration curve for determining by means of IR
spectroscopy the content of versatic acid in a solution of
Nd(Vers).sub.3.
FIG. 2b. A calibration curve for determining by means of IR
spectroscopy the content of water in a solution of
Nd(Vers).sub.3.
FIG. 3. The spectrum in the visible region of a cyclohexane
solution of pure Nd(Vers).sub.3 (dotted line) and the spectrum
obtained after the addition of versatic acid (broken line,
Nd(Vers).sub.3/VersH molar ratio 1:1.47).
FIG. 4. A calibration curve for determining, through visible
spectroscopy, the content of versatic acid in a solution of
Nd(Vers).sub.3, whose construction is described in the examples of
the present patent application (- -.box-solid.- -).
An object of the present invention therefore relates to a method
for the purification of a hydrocarbon solution deriving from the
synthesis of a lanthanide carboxylate, containing said carboxylate
and impurities of the corresponding carboxylic acid and/or water,
which comprises at least one of the following steps:
a) treating the hydrocarbon solution, containing the lanthanide
carboxylate, with an aqueous solution of a base so as to obtain a
pH of the aqueous phase ranging from 9.0 to 12.2;
b) treating the hydrocarbon solution containing the lanthanide
carboxylate with a solid selected from Na.sub.2SO.sub.4,
MgSO.sub.4, Mg(ClO.sub.4).sub.2, molecular sieves 3 .ANG.,
molecular sieves 4 .ANG., molecular sieves 5 .ANG. and molecular
sieves 13 X.
If the solution containing the carboxylate is subjected to both
forms of treatment, the treatment of step (a) is first carried out
and the resulting solution is then subjected to the treatment of
step (b).
In step (a) the base solution is added to the hydrocarbon solution
until the pH value of the aqueous phase remains stably within the
range claimed. The pH of the aqueous phase is preferably included
within the range of 10.5-12.0, even more preferably between 11.0
and 11.8. The aqueous solution used, containing the base,
preferably has a concentration ranging from 0.01 to 2 M. At the end
of the treatment of step (a), the organic phase is separated from
the aqueous phase.
The selection, in step (a), of the particular pH range claimed,
allows the purification of a hydrocarbon solution containing a
lanthanide carboxylate by means of salification and removal from
said organic phase of the carboxylic acid in excess or possibly
non-reacted, at the end of the synthesis of the lanthanide
carboxylate which uses this acid as starting reagent. It is
completely unexpected that by putting the hydrocarbon solutions
containing a lanthanide carboxylate in contact with a strongly
basic aqueous phase, in accordance with the process of the present
invention, the stability of said solutions is not influenced, as
insoluble products are not formed and there is also no formation of
mixed products, in which a fraction of the carboxylate ligands,
initially present on the lanthanide, is substituted by oxide or
hydroxide groups.
The following bases can be used in step (a) of the present
invention: hydroxides and oxides of alkaline and alkaline-earth
metals, ammonia and organic amines such as, for example, methyl
amine, dimethyl amine, trimethyl amine, ethyl amine, propyl amine,
butyl amine, pyridine. According to a preferred aspect sodium
hydroxide or potassium hydroxide are used, even more preferably
sodium hydroxide.
The hydrocarbon solution is preferably a cyclohexanic solution.
The carboxylic acids which can be removed, by means of the process
of the present invention, from the solutions of the corresponding
lanthanide carboxylate, can be C2-C40 acids, selected from
aliphatic, cyclo-aliphatic, alicyclic and aromatic, mono- and
polycarboxylic, preferably C6-C20, even more preferably C8-C12.
Typical examples of acids which can be treated with the process of
the present invention, are acetic acid, propionic acid, butyric
acid, isobutyric acid, pivalic acid, 2-methyl butanoic acid,
3-methyl butanoic acid, cyclohexane carboxylic acid,
1,4-cyclohexane dicarboxylic acid, 1,2-cyclohexane dicarboxylic
acid, benzoic acid, cyclohexyl acetic acid, phenyl acetic acid,
3,5-dimethyl hexanoic acid, 2-ethyl hexanoic acid, 3-ethyl hexanoic
acid, octanoic acid, iso-octanoic acid, versatic acid (blend of
carboxylic acids which can be found on the market with a
predominant C10 fraction and with an acid number generally ranging
from 310 to 325 mg KOH/g), naphthenic acids (blend of carboxylic
acids which can be found on the market with an acid number
generally ranging from 160 to 300 g KOH/g), lauric acid, palmitic
acid, stearic acid, oleic acid, linoleic acid.
The acids are preferably: versatic acid, naphthenic acid and
2-ethyl hexanoic acid. Impurities of other carboxylic acids
possibly present in solution, such as, for example, acetic acid,
propionic acid, butyric acid, stearic acid, present individually or
in a mixture thereof, in solutions of, for example, neodymium
versatate, neodymium naphthenate or neodymium 2-ethyl hexanoate,
are also efficaciously removed from the hydrocarbon solution by
means of the process of the present invention.
The lanthanide carboxylate solutions which can be treated with the
method of the present invention can be, for example, solutions of
neodymium, praseodymium, gadolinium, lanthanum carboxylates and any
mixture thereof. In particular the hydrocarbon solutions containing
neodymium versatate, neodymium naphthenate, neodymium
2-ethyl-hexanoate can be suitably treated with the process of the
present invention.
Step b) allows the purification of the hydrocarbon solution of
lanthanide carboxylate by removing the water contained in said
solutions. The hydrocarbon solution is preferably a cyclohexanic
solution. The solid materials used in step b) are added directly to
said hydrocarbon solution: their complete insolubility under these
conditions and the fact that their reaction with H.sub.2O does not
generate other products, guarantee that there is no pollution of
the lanthanide carboxylate solutions.
Surprisingly, the treatment of step b) does not cause precipitation
or physical or chemical adsorption of the metal on the solid
surface, the whole quantity of lanthanide carboxylate which is
present, remains in solution.
The molecular sieves 3 .ANG. are characterized by the formula
K.sub.nNa.sub.12-n[(AlO.sub.2).sub.12(SiO.sub.2).sub.12], the
molecular sieves 4 .ANG. by the formula
Na.sub.12[(AlO.sub.2).sub.12(SiO.sub.2).sub.12], the molecular
sieves 5 .ANG. by the formula
Ca.sub.nNa.sub.12-2n[(AlO.sub.2).sub.12(SiO.sub.2).sub.12] and the
molecular sieves 13X by the formula
Na.sub.86[(AlO.sub.2).sub.86(SiO.sub.2).sub.106]. According to a
preferred aspect of the present invention, molecular sieves 3
.ANG., molecular sieves 4 .ANG. or a mixture thereof are used, even
more preferably molecular sieves 3 .ANG. are adopted.
The quantity of H.sub.2O expressed as moles/liter, initially
present in the lanthanide carboxylate solutions depends on the
synthesis method used and, as water chemically binds with the
carboxylate, it also depends on the concentration of the
lanthanide. It may therefore be more significant to express the
amount of water present in the solution as the molar ratio
H.sub.2O/Ln and consequently the latter can vary from 0.5 to values
of around 1.4-1.5. All these solutions can be easily treated,
according to the process of the present invention, until a much
lower molar H.sub.2O/Ln ratio than the starting ratio, is obtained
at the end of the treatment.
The quantity of residual H.sub.2O in the hydrocarbon solutions of
the lanthanide carboxylates, diminishes with the increase of the
initial weight ratio between H.sub.2O and solid product used and of
the contact time between solid and solution. Consequently,
according to a preferred aspect of the present invention, the
hydrocarbon solution containing the lanthanide carboxylate is
circulated in continuous, by using a suitable pump, through a
column having appropriate dimensions, filled with one of the solid
products described in step b). Molecular sieves 3 .ANG., molecular
sieves 4 .ANG. or a mixture thereof are preferably used, even more
preferably molecular sieves 3 .ANG. are adopted.
Steps a) and/or b) of the process of the present invention can be
repeated several times to obtain the desired purity degree of the
lanthanide carboxylate solution as far as the water and/or
carboxylic acid content is concerned.
With the method of the present invention, it is possible to obtain
hydrocarbon solutions of lanthanide carboxylate wherein the molar
ratios between lanthanide and protogenic substances, such as water
and carboxylic acid, are in the range of detection limit of normal
analytical techniques, typically: Ln/H.sub.2O>60 and
Ln/RCOOH>100. The solutions obtained according to the process of
the present invention can be used as such for subsequent
polymerization processes without requiring the high vacuum solvent
evaporation steps as described in the prior documents. Furthermore,
it has been found that, unexpectedly with respect to what is
described in U.S. Pat. No. 6,111,082, the cyclohexane solutions of
lanthanide carboxylate, in particular neodymium versatate, obtained
through the purification process of the present invention, wherein
water and acid are practically absent, have proved to be
indefinitely stable with time and, in practice, also after several
weeks no precipitation of product is observed. The stable
cyclohexane solutions thus obtained, characterized by
Ln/H.sub.2O>60 and Ln/RCOOH>100, represent a further object
of the present invention and are directly used in the
polymerization of conjugated dienes, for example isoprene or
butadiene, preferably butadiene, giving better performances in
terms of molecular weight, which is lower, and reaction kinetics
which are faster.
The purification methods described above can be used for any
lanthanide carboxylate solution containing carboxylic acid and/or
water, regardless of the synthesis method used. According to the
method of the present invention, cyclohexane solutions of
Nd(Vers).sub.3 can be treated, obtained by reaction of
Nd.sub.2O.sub.3 and versatic acid, as described, for example, in
U.S. Pat. No. 5,686,371 EP 0,562,081 or EP 0,968,992. Similarly,
cyclohexane solutions of Nd(Vers).sub.3 can be treated, obtained by
the reaction of NdCl.sub.3 with Na(Vers), as described, for
example, in U.S. Pat. No. 4,520,177 or U.S. Pat. No. 6,111,082. The
possibility of having solutions of lanthanide carboxylates with a
water and/or versatic acid content which can be regulated, using
the method of the present invention, until product samples are
obtained practically free of water and carboxylic acid, also
allows, if necessary, the preparation, by a simple evaporation of
the solvent at reduced pressure, using normal equipment well-known
to the experts in the field, of lanthanide solid carboxylates
having a purity degree corresponding to that of the starting
solution.
The achievement of the desired purity degree can be followed and
controlled by means of new analysis methods based on the use of
suitable and particular parameters of IR spectroscopy or
spectroscopy in the visible region.
In particular, new methods allow the quantity of carboxylic acid
and/or water directly present in the solutions containing
lanthanide carboxylates to be measured, after suitable
calibrations, in a non-destructive manner.
With reference to IR spectroscopy, it has in fact been found that
in the IR spectra and more specifically in the region between 1800
and 1475 cm.sup.-1, the addition of progressive amounts of
carboxylic acid to reference hydrocarbon solutions of the
corresponding pure lanthanide carboxylate, causes a decrease in the
intensity of the band at 1514 cm.sup.-1, which is characteristic of
lanthanide carboxylate and corresponding to the carboxylate ligand
which is bridge-bounded to three lanthanide centres, and the
parallel increase of an absorption band at 1560 cm.sup.-1, together
with two bands at 1663 and 1700 cm.sup.-1.
The band at 1560 cm.sup.-1 was attributed to the carboxylate ligand
bridge-bounded between two lanthanide centres, whereas the two
bands at 1663 and 1700 cm.sup.-1 were attributed to the carboxylic
acid coordinated to a single lanthanide center and to the free
carboxylic acid in excess, respectively.
The areas of the absorbing bands centred at 1700 and 1663
cm.sup.-1, for each of the reference solutions, divided by the
concentration of the lanthanide present in each of the reference
solutions, is indicated in a graph with respect to the
corresponding carboxylic acid/lanthanide molar ratio: the curve
thus obtained allows the calculation of the carboxylic acid content
of any solution deriving from the synthesis of the corresponding
lanthanide carboxylate, containing the carboxylate and said acid as
impurity.
It has been found that the addition of water to hydrocarbon
solutions of the corresponding pure lanthanide carboxylate, causes,
in the IR spectra, a decrease in the intensity of the 1514
cm.sup.-1 band, characteristic of lanthanide carboxylate and
corresponding to the carboxylate ligand which is bridge-bounded
with three lanthanide centres, and the parallel increase of an
absorption band at 1560 cm.sup.-1, together with a band at 1685
cm.sup.-1. The band at 1560 cm.sup.-1 was attributed to the
carboxylate ligand which is bridge-bounded between two lanthanide
centres, whereas the 1685 cm.sup.-1 band was attributed to the
carboxylate reversibly protonated by water, with the formation of
carboxylic acid coordinated to neodymium.
The area of the absorption band centred at 1685 cm.sup.-1, for each
of the reference solutions, divided by the molar concentration of
the lanthanide present in the solution, is shown in a graph with
respect to the corresponding H.sub.2O/lanthanide molar ratio. The
curve allows the calculation of the water content of any solution
deriving from the synthesis of a lanthanide carboxylate containing
water as impurity.
In accordance with the above, an object of the present invention
relates to a method for determining the content of carboxylic acid
and/or water of a solution of the corresponding lanthanide
carboxylate, containing said acid and/or water as impurities, which
comprises the following steps:
1) measuring the molar concentration of lanthanide in the solution
[Ln]
2) recording the IR spectrum of the solution and calculating the
IA/[Ln] ratio, by dividing the area corresponding to the absorption
within the range 1750-1600 cm.sup.-1 (IA), resolved before in the
relative water and acid bands, if both are present, by the molar
concentration of lanthanide,
3) obtaining, for the value or the values obtained in the previous
item 2) the corresponding value of the carboxylic acid/lanthanide
and/or water/lanthanide molar ratio making use of the relative
calibration curve constructed by indicating, in the abscissa, the
different carboxylic acid/lanthanide or water/lanthanide molar
ratios of reference solutions containing known amounts of
carboxylic acid and lanthanide or water and lanthanide, and, in the
ordinate, the values of the ratio IA/[Ln] corresponding to those
reference solutions, wherein IA is the area of the absorbing IR
bands within the range of 1750-1600 cm.sup.-1 for each reference
solution, recorded under the same conditions as step 2), and [Ln]
is the relative lanthanide concentration.
According to a preferred aspect of the present invention, it is
therefore possible, in particular, to determine the content of
carboxylic acid of a solution of the corresponding lanthanide
carboxylate containing said acid as impurity, by means of a method
comprising the following steps:
1) measuring the molar concentration of lanthanide in the solution
[Ln]
2) recording the IR spectrum of the solution and calculating the
IA/[Ln] ratio, by dividing the area of the absorption bands centred
at 1700 and 1663 cm.sup.-1 (IA) by the molar concentration of
lanthanide,
3) obtaining, for the value obtained in the previous item 2), the
corresponding value of the carboxylic acid/lanthanide molar ratio,
which can be converted into the relative moles of carboxylic acid
by multiplying by [Ln], with the use of a calibration curve
constructed by indicating, in the abscissa, the different
carboxylic acid/lanthanide molar ratios of reference solutions
containing known amounts of carboxylic acid and lanthanide, and, in
the ordinate, the values of the ratio IA/[Ln] corresponding to
those reference solutions, wherein IA is the area of the absorbing
IR bands centred at 1700 and 1663 cm.sup.-1 for each reference
solution, recorded under the same conditions as step 2), and [Ln]
is the relative lanthanide concentration.
The preparation of the reference solutions of lanthanide
carboxylate containing different and controlled amounts of
carboxylic acid as impurity, can be effected by means of any known
method.
The same conditions, in particular the same cell at a known depth,
must be used for recording the IR spectrum in step 2) and the IR
spectra for preparing the calibration curve in step 3).
The method described above is preferably used for solutions
containing neodymium carboxylate as lanthanide carboxylate. For a
better understanding of what is described above, FIG. 1 shows, in
particular, the IR spectrum of a cyclohexanic solution of pure
Nd(Vers).sub.3 (dotted line) and the IR spectrum obtained after the
addition, to the same solution, of versatic acid (broken line,
Nd(Vers).sub.3/VersH molar ratio 1:1.47), whereas FIG. 2a shows a
calibration curve for determining, by IR spectroscopy, the content
of versatic acid in a solution of Nd(Vers).sub.3, whose
construction is described in the examples appearing in the
experimental part of the present patent application.
According to another preferred aspect of the present invention, it
is possible, in particular, to determine the content of water of a
solution containing a lanthanide carboxylate and water as impurity,
by means of a method which includes the following steps:
1) measuring the molar concentration of lanthanide in the solution
[Ln]
2) recording the IR spectrum of the solution and calculating the
IA/[Ln] ratio by dividing the area of the absorption band centred
at 1685 cm.sup.-1 (IA) by the molar concentration of
lanthanide,
3) obtaining, for the value obtained in the previous item 2), the
corresponding value of the water/lanthanide molar ratio, which can
be converted into the relative moles of water, by multiplying by
[Ln], with the use of a calibration curve constructed by
indicating, in the abscissa, the different water/lanthanide molar
ratios of reference solutions containing known amounts of water and
lanthanide, and, in the ordinate, the values of the IA/[Ln] ratio
corresponding to those reference solutions, wherein IA is the area
of the absorbing IR band centred at 1685 cm.sup.-1 for each
reference solution, recorded under the same conditions as step 2),
and [Ln] is the relative lanthanide concentration.
The preparation of reference solutions of lanthanide carboxylate
containing different and controlled amounts of water as impurity,
can be effected using any known method.
The same conditions, in particular the same cell at a known depth,
must be used for recording the IR spectrum in step 2) and the IR
spectra for preparing the calibration curve in step 3).
The method described above for measuring the water content, is
preferably used for solutions containing neodymium carboxylate. For
a better understanding of what is described above, FIG. 1 shows, in
addition to the IR spectrum of a cyclohexanic solution of pure
Nd(Vers).sub.3 (dotted line), the IR spectrum obtained after the
addition of water, to the same solution, (continuous line,
Nd(Vers).sub.3/H.sub.2O molar ratio 1:1.5), whereas FIG. 2a shows a
calibration curve for determining, by IR spectroscopy, the content
of water in a solution of Nd(Vers).sub.3, whose construction is
described in the examples of the present patent application.
It is possible to obtain the profile of the spectrum within the
range 1750-1600 cm.sup.-1 of lanthanide carboxylate samples
containing unknown amounts of carboxylic acid and water, for
example neodymium carboxylate, in the various component bands, by
means of a simple mathematical "curve-fitting" procedure (effected
by means of common software for the elaboration of spectra known to
technical experts, such as that described in GRAMS/AI of Thermo
Electron Corporation): carboxylic acid and water are clearly
calculated from the area of the bands thus obtained, on the basis
of the calibration curves previously prepared.
The attainment of the desired purity degree for solutions of
lanthanide carboxylates can be also detected and controlled by
means of a new analysis method based on the use of particular and
suitable spectroscopy parameters in the visible region.
In particular, the method allows, after suitable calibration, the
calculation of the amount of carboxylic acid and/or water contained
directly in solutions of lanthanide carboxylates, in a
non-destructive way: the Applicant has found, in fact, that in the
absorption spectra in the visible and near infrared region, in
particular in the area of 400 and 950 nm, where normally each
lanthanide has the electronic absorption bands, relating to the f-f
transitions, the progressive addition of water and/or carboxylic
acid to hydrocarbon solutions of the corresponding pure lanthanide
carboxylate, cause a considerable increase in intensity of said
lanthanide carboxylate bands. The variation in intensity was
interpreted as evidence of the different type of coordination of
the carboxylate ligands at the center of the lanthanide, caused by
the reaction with water and carboxylic acid, i.e. to the variation
in the type of coordination of the carboxylate ligand, from
bridge-bounded with three lanthanide centres to bridge-bounded
between two lanthanide centres or coordinated on a single
lanthanide centre. The value of the areas of the bands of the
spectrum, in particular the most intense band, therefore provides
the measurement of the quantity of acid and/or water present in the
lanthanide carboxylate solution.
An object of the present invention therefore relates to a method
for determining the content of carboxylic acid and/or water of a
solution of the corresponding lanthanide carboxylate containing
said acid and/or water as impurities, which comprises the following
steps:
1) measuring the molar concentration of lanthanide in the solution
[Ln]
2) recording the visible spectrum of the solution and calculating
the IA/[Ln] ratio by dividing the area of one of the bands of the
lanthanide carboxylate spectrum (IA), preferably the most intense
band, by the molar concentration of lanthanide,
3) obtaining, for the value obtained in the previous item 2), the
corresponding value of the carboxylic acid/lanthanide and/or
water/lanthanide molar ratio, with the use of a calibration curve
constructed by indicating, in the abscissa, the different
carboxylic acid/lanthanide or water/lanthanide molar ratios of
reference solutions containing known amounts of carboxylic acid and
lanthanide or water and lanthanide, and, in the ordinate, the
values of the IA/[Ln] ratio corresponding to those reference
solutions, wherein IA is the area, for each reference solution, of
the band which is at the same wave-length as that used in step 2)
and which has been recorded under the same conditions as step 2),
and [Ln] is the relative lanthanide concentration.
According to a preferred aspect of the present invention, it is
possible, in particular, to determine the content of carboxylic
acid of a solution of the corresponding lanthanide carboxylate
containing said acid as impurity, which comprises the following
steps:
1) measuring the molar concentration of lanthanide in the solution
[Ln]
2) recording the visible spectrum of the solution and calculating
the IA/[Ln] ratio by dividing the area of one of the bands present
in the spectrum of lanthanide carboxylate (IA), preferably the most
intense band, by the molar concentration of lanthanide,
3) obtaining, for the value obtained in the previous item 2), the
corresponding value of the carboxylic acid/lanthanide molar ratio,
which can be converted into the relative moles of acid, by
multiplying by [Ln], with the use of a calibration curve
constructed by indicating, in the abscissa, the different
carboxylic acid/lanthanide molar ratios of reference solutions
containing known amounts of carboxylic acid and lanthanide, and, in
the ordinate, the values of the IA/[Ln] ratio corresponding to
those reference solutions, wherein IA is the area of each reference
solution, of the band at the same wave-length as that used in step
2), recorded under the same conditions as step 2), and [Ln] is the
relative lanthanide concentration.
The preparation of the reference solutions of lanthanide
carboxylate containing different and controlled amounts of
carboxylic acid as impurity, can be effected by means of any known
method.
The same conditions, in particular the same cell at a known depth,
must be used for the recording the visible spectrum in step 2) and
the visible spectra for preparing the calibration curve in step
3).
In particular, for neodymium the band preferably used for obtaining
a measurement of the amount of carboxylic acid in a solution of
neodymium carboxylate, is that centred around 584 nm, [assigned to
the transition of
.sup.4G.sub.5/2(.sup.2G.sub.7/2).rarw..sup.4I.sub.9/2 according to
what is shown in A. Kumar, D. K. Rai and S. B. Rai, Spectrochimica
Acta Part A, volume 58 (2002), pages 1379-1387].
FIG. 3 shows the spectrum in the visible region of a cyclohexane
solution of pure Nd(Vers).sub.3 (dotted line) and the spectrum
obtained after the addition of versatic acid (broken line,
Nd(Vers).sub.3/VersH molar ratio 1:1.47).
FIG. 4 shows a calibration curve for determining, through visible
spectroscopy, the content of versatic acid in a solution of
Nd(Vers).sub.3, whose construction is described in the examples of
the present patent application (- -.box-solid.- -).
According to another preferred aspect of the present invention, it
is possible to determine the water content of a solution of
lanthanide carboxylate containing water as impurity, which includes
the following steps:
1) measuring the molar concentration of lanthanide in the solution
[Ln]
2) recording the visible spectrum of the solution and calculating
the IA/[Ln] ratio by dividing the area of one of the bands present
in the spectrum of the lanthanide carboxylate (IA) considered,
preferably the most intense band, by the molar concentration of
lanthanide,
3) obtaining, for the value obtained in the previous point 2) the
corresponding molar ratio H.sub.20/lanthanide, using the
calibration curve constructed by indicating, in the abscissa, the
different water/lanthanide molar ratios of reference solutions
containing known quantities of water and lanthanide, and, in the
ordinate, the values of the IA/[Ln] ratio corresponding to those
reference solutions, wherein IA is the area of each reference
solution, of the band at the same wave-length as that used in step
2), recorded under the same conditions as step 2), and [Ln] is the
relative lanthanide concentration.
The same conditions, in particular the same cell at a known depth,
must be used for recording the visible spectrum in step 2) and the
spectra for preparing the calibration curve in step 3).
The preparation of the reference solutions of lanthanide
carboxylate containing different and controlled amounts of water as
impurity, can be effected by means of any known method.
In particular, also in this case, for neodymium the band preferably
used is that centred around 584 nm, [assigned to the transition of
.sup.4G.sub.5/2(.sup.2G.sub.7/2).rarw..sup.4I.sub.9/2 according to
what is indicated in A. Kumar, D. K. Rai and S. B. Rai,
Spectrochimica Acta Part A, volume 58 (2002), pages 1379-1387].
FIG. 3 shows the spectrum in the visible region of a cyclohexane
solution of pure Nd(Vers).sub.3 (dotted line) and the spectrum
obtained after the addition of water to the same solution (broken
line, Nd(Vers).sub.3/H.sub.2O molar ratio 1:1.5).
FIG. 4 shows a calibration curve for determining, through visible
spectroscopy, the content of water in a solution of Nd(Vers).sub.3,
whose construction is described in the examples of the present
patent application (- -.diamond-solid.- -).
When water and versatic acid are both present, the upper and lower
limit of the sum of relative molar concentrations can be estimated,
using the acid curve, whose effect is weaker and the water curve,
whose effect is stronger, respectively. When both water and acid
are contained in the solutions as impurities, the greater the
difference in concentration between water and acid, the more
accurate the evaluation of their concentrations will be by means of
visible spectroscopy.
A further object of the present invention relates to the
purification process of the present invention wherein the initial
content of hydrocarbon solution deriving from the synthesis of
lanthanide carboxylate in terms of water or carboxylic acid and/or
the attainment of the desired purity in terms of water or
carboxylic acid content, are followed, controlled and verified by
means of one or more of the analytical methods claimed above.
EXAMPLES
The analytical techniques and characterization methods briefly
described and listed hereunder were used in the following
examples.
The measurements effected by means of IR spectroscopy mentioned in
the following examples were carried out by means of a transmission
spectrophotometer Nicolet Nexus, using a cell for liquids having an
optical path equal to 0.005 cm, equipped with windows of CaF.sub.2
and charging the solutions under anhydrous conditions.
The measurements effected by means of visible spectroscopy and
mentioned in the following examples, were carried out by means of a
Perkin Elmer spectrophotometer (.LAMBDA.-19 model) using Suprasil
quartz cells with an optical path of 1 cm and a screw-stopper or
tap to allow the charging and preservation of the sample under
anhydrous conditions.
The molecular weight measurements of the polymers was effected by
means of Gel-Permeation chromatography (GPC). The analyses of the
samples were carried out in tetrahydrofuran (stabilized with
Irganox) at 40.degree. C., using a Waters differential
refractometer as detector. The chromatographic separation was
obtained with a set of PL-MIXED columns, by establishing a
flow-rate of the eluent of 1 ml/min. The data were acquired and
processed by means of Maxima 820 software version 3.30 (Millipore)
and the molecular mass determination was effected according to the
universal calibration method (k=0.000212 .alpha.=0.739).
The determination of the content of 1,4-cis, 1,4-trans and
1,2-units in the polybutadienes produced was effected by means of
the known techniques based on IR spectroscopy.
The commercial reagents listed below were used in the preparations
described in the examples:
TABLE-US-00001 neodymium oxide Nd.sub.2O.sub.3 STREM neodymium
carbonate (Nd.sub.2(CO.sub.3).sub.3 STREM hydrochloric acid HCl
(normex) C.ERBA sodium hydroxide NaOH (normex) C.ERBA molecular
sieves (3 .ANG.) ALDRICH basic alumina (pellets) ALDRICH versatic
acid SHELL 1,3 butadiene (99.95%) RIVOIRA diisobutylaluminum
hydride Al(iso-Bu).sub.2H DIBAH ALDRICH diisobutylaluminum chloride
Al(iso-Bu).sub.2Cl DIBAC ALDRICH
The reagents and/or solvents used and not indicated above are those
commonly used in laboratory techniques and on an industrial scale
and can be easily found at the premises of commercial operators
specialized in the field.
Example 1
Preparation of Nd(Vers).sub.3 from NdCl.sub.3 and NaVers
a) Preparation of an Aqueous Solution of NdCl.sub.3
4.21 g of Nd.sub.2O.sub.3 (25.02 mgA) and 20 ml of H.sub.2O are
charged into a 250 ml flask, equipped with magnetic stirring. The
mixture is amalgamated by leaving it under light stirring for about
10 min., after which 73.9 ml of HCl (1M) are added, by means of a
dosage burette and the whole mixture is kept under stirring at room
temperature for 3 h. At the end of this phase, a slightly turbid
light-blue coloured aqueous solution is obtained, having a pH=6.9.
After being filtered to eliminate traces of non-reacted
Nd.sub.2O.sub.3, the solution is brought to volume in a 250 ml
calibrated flask and used in the preparations described hereunder
[Nd]=0.0985 (99.4% yield with respect to HCl).
b) Preparation of an Aqueous Solution of Sodium Versatate
(NaVers)
12.7 g of versatic acid (73.7 mmoles) and about 20 ml of H.sub.2O
are charged into a 250 ml flask, equipped with a magnetic stirrer,
two phases are formed due to the poor solubility of versatic acid
in water. 73.9 ml of NaOH (1M) are added, in about 30 minutes, to
the mixture maintained under stirring at room temperature, thus
obtaining a slightly opalescent aqueous solution having a pH=11.4.
The solution is then filtered and brought to volume in a calibrated
flask and used in the preparations described hereunder.
[Na(Vers)]=0.296 M, calculated by the NaOH equivalents used.
c) Preparation of Nd(Vers).sub.3
80 ml of an aqueous solution of NdCl.sub.3 ([Nd]=0.0985 M, 7.88
mmoles), obtained as described in the previous point (a) and 80 ml
of cyclohexane are transferred to a 250 ml flask, equipped with a
magnetic stirrer. 79.5 ml of aqueous solution of NaVers (23.5
mmoles), prepared as described under point (b), are added, by means
of a drip funnel, to the mixture thus obtained, maintained under
stirring at room temperature. At the end of the addition, the
mixture is stirred vigorously for a further 10 minutes and then
transferred to a separating funnel. After decanting, the underlying
aqueous phase is eliminated and the residual organic phase is
washed with water (2.times.50 ml). By operating in this way, 75 ml
of a cyclohexane solution of Nd(Vers).sub.3 having [Nd]=0.089 M,
are recovered.
Example 2a
Construction of a Calibration Curve for Determining by Means of
Visible Spectroscopy the Content of Water or Versatic Acid in a
Solution of Nd(Vers).sub.3
The solid Nd(Vers).sub.3 used in this example, was prepared by
drying the cyclohexane solution prepared in the previous example 1
and drying the product obtained under high vacuum at 60-80.degree.
C. for 18 hours.
The solid sample resulting from this drying treatment has
H.sub.2O/Nd.ltoreq.0.002 (molar ratio), obtained with "Karl Fisher"
titration and VersH/Nd.ltoreq.0.001 (molar ratio), obtained with
acid-base titration.
0.3139 g of solid Nd(Vers).sub.3, obtained as described above and
9.225 g of cyclohexane are charged into a tailed Schlenk-tube
equipped with a magnetic stirrer. The mixture is left under
stirring for 24 hours at room temperature in order to obtain a
homogeneous solution with [Nd]=0.042 M. Six equal portions of the
solution thus obtained are introduced into the same number of
tailed Schlenk-tubes equipped with a magnetic stirrer and to each
Schlenk-tube, the appropriate quantity of versatic acid is added,
by means of a micro-syringe. The solutions thus prepared have a
content of versatic acid, calculated as a molar ratio VersH/Nd,
varying from 0 to 1.47, in particular, in the various solutions,
the molar ratio VersH/Nd is equal to 0.0-0.10-0.22-0.55-0.80-1.47.
After maintaining them under stirring at room temperature for 15
minutes, they are transferred to the specific quartz cells and the
spectrum from 500 to 700 nm is registered. The absorption band area
centred at 584 nm (AI (584)), divided by the molar concentration of
Nd present ([Nd]), is indicated in a graph with respect to the
VersH/Nd molar ratio, for the various solutions analyzed. The
results obtained are specified in FIG. 4, where [A] refers to
[VersH], together with the corresponding calibration curve of the
equation Y.sub.acid=-12.13X.sup.2+77.21X+71.47 (- -.box-solid.-
-).
With a completely analogous procedure to that described above,
seven cyclohexane solutions of Nd(Vers).sub.3 are prepared with
[Nd]=0.042 M having a H.sub.2O content, calculated as H.sub.2O/Nd
molar ratio, varying from 0 to 1.5, in particular, in the various
solutions, the H.sub.2O/Nd molar ratio is equal to
0.0-0.12-0.20-0.50-0.80-1.00-1.50, and the spectrum from 500 to 700
nm is registered. Also in this case, the absorption band area
centred at 584 nm, divided by the molar concentration of Nd
present, is indicated in a graph with respect to the H.sub.2O/Nd
molar ratio, for the various solutions analyzed.
The results obtained are specified in FIG. 4, where [A] refers to
[H.sub.2O], together with the corresponding calibration curve of
the equation Y.sub.H2O=-76.13X.sup.2+210.61X+76.32 (-
-.diamond-solid.- -).
The curves indicated in FIG. 4 allow the [A]/[Nd] molar ratio to be
determined, by means of visible spectroscopy, wherein A=versatic
acid or H.sub.2O, in cyclohexane solutions of Nd(Vers).sub.3, by
knowing the relative value of the absorption band area centred at
584 nm AI(584) measured under the same conditions used for the
construction of the calibration curve.
Example 2b
Construction of a Calibration Curve for Determining by Means of IR
Spectroscopy the Content of Water or Versatic Acid in a Solution of
Nd(Vers).sub.3
The solid Nd(Vers).sub.3 used in this example, was prepared by
drying the cyclohexane solution prepared in the previous example 1
and drying the product obtained under high vacuum at 60-80.degree.
C. for 18 hours.
The solid sample resulting from this drying treatment has
H.sub.2O/Nd.ltoreq.0.002 (molar ratio), obtained with "Karl Fisher"
titration and VersH/Nd.ltoreq.0.001 (molar ratio), obtained with
acid-base titration.
0.3921 g of solid Nd(Vers).sub.3, prepared as described above and
10.837 g of cyclohexane are charged into a tailed Schlenk-tube
equipped with a magnetic stirrer. The mixture is left under
stirring for 24 hours at room temperature in order to obtain a
homogeneous solution with [Nd]=0.044 M. Following the same
procedure described in example 1, the solution thus obtained is
divided into five equal parts and a known quantity of versatic acid
is added to each portion so that the molar ratio VersH/Nd varies
from 0.1 to 1.5, in particular, in the various solutions, the molar
ratio VersH/Nd is equal to 0.10-0.22-0.55-0.80-1.47. Finally, the
spectrum of the various solutions in the area between 1800 and 1450
cm.sup.-1 is registered. The absorption band area centred at 1700
and 1663 cm.sup.-1, divided by the molar concentration of Nd
present, is subsequently indicated in a graph with respect to the
VersH/Nd molar ratio, for the various solutions analyzed. The
results obtained are specified in FIG. 2a, together with the
corresponding calibration curve of the equation
Y.sub.acid=61.40X-2.77.
With a completely analogous procedure to that described above, six
cyclohexane solutions of Nd(Vers).sub.3 are prepared with
[Nd]=0.044 M having a H.sub.2O content, calculated as H.sub.2O/Nd
molar ratio, varying from 0.1 to 1.4, in particular, in the various
solutions, the H.sub.2O/Nd molar ratio is equal to
0.12-0.25-0.50-0.80-1.00-1.40, and the IR spectrum from 1800 to
1450 cm.sup.-1 is registered. The area of the absorption band
centred at 1685 cm.sup.-1, divided by the molar concentration of Nd
present, is indicated in a graph with respect to the H.sub.2O/Nd
molar ratio, for the various solutions analyzed.
The results obtained are specified in FIG. 2b, together with the
corresponding calibration curve of the equation
Y.sub.H2O=23.29X+2.22.
The curves indicated in FIGS. 2a and 2b allow the [A]/[Nd] molar
ratio to be determined, by means of IR spectroscopy, wherein
A=versatic acid or H.sub.2O, in cyclohexane solutions of
Nd(Vers).sub.3, once the relative IR absorption has been measured
under the same conditions.
Example 3
Preparation of Nd(Vers).sub.3 from Nd.sub.2O.sub.3 and Versatic
Acid
(a) The following products are charged in order into a 250 ml
flask, equipped with a magnetic stirrer and a bubble cooler: 7.21 g
of Nd.sub.2O.sub.3 (42.85 mgA), 29.52 g of versatic acid (171.4
mmoles), 100 ml of cyclohexane and a catalytic quantity of HCl
(37%). The reaction mixture is then heated to the reflux
temperature of the solvent for about 3 hours. In this phase, all of
the solid present in the reaction container almost totally
dissolves and a deep blue-purple-coloured solution is obtained,
having [Nd]=0.42 M. The IR spectrum between 1880 and 1450 cm.sup.-1
and the Visible spectrum between 500 and 700 nm of this solution
are measured, under the same conditions and with the same equipment
as examples 2a and 2b, and the results obtained are indicated on
the calibration curves of examples 2a and 2b, providing the
following results: VersH/Nd=0.9 (molar ratio); H.sub.2O/Nd=1.2
(molar ratio). The versatic acid and water analyses are repeated
with the known invasive acid-base titration and "Karl Fisher"
titration methods respectively, and the results, substantially
confirming those measured with the spectroscopic methods of the
present invention, are as follows: VersH/Nd=0.9 (molar ratio);
H.sub.2O/Nd=1.3 (molar ratio). (b) A part of the solution
previously obtained, is treated, under vigorous stirring, with a
solution of NaOH (0.1 M) until the pH value of the aqueous phase is
stably maintained at 11.5. After 2 hours, the phases are separated,
the organic phase is washed with two 20 ml fractions of H.sub.2O
and 40 ml of a cyclohexane solution of Nd(Vers).sub.3 are obtained,
having [Nd]=0.41 M: the IR spectrum between 1880 and 1450 cm.sup.-1
and the Visible spectrum between 500 and 700 nm of this solution
are measured, under the same conditions and with the same equipment
as examples 2a and 2b, and the results obtained are indicated on
the calibration curves of examples 2a and 2b, providing the
following results: VersH/Nd=0.012 (molar ratio); H.sub.2O/Nd=1.3
(molar ratio).
Example 4
Preparation of Nd(Vers).sub.3 from Nd.sub.2(CO.sub.3).sub.3 and
Versatic Acid
The following products are charged in order into a 250 ml flask,
equipped with a magnetic stirrer and a bubble cooler: 8.15 g of
Nd.sub.2(CO.sub.3).sub.3 (34.79 mgA), 22.16 g of versatic acid
(128.7 mmoles), 100 ml of cyclohexane and a catalytic quantity of
HCl (37%). Operating as described above in example 3, a
blue-purple-coloured cyclohexane solution is obtained, which is
accompanied, in this case, by a vigorous development of gas. The
reaction mixture is then cooled to room temperature and, a solution
of NaOH (1 M) is added, under vigorous stirring, until the pH value
of the aqueous phase is stably maintained at 10.5. After 2 hours,
the phases are separated, the organic phase is washed with two 20
ml fractions of H.sub.2O and 95 ml of a cyclohexane solution of
Nd(Vers).sub.3 are obtained, which is put in contact with molecular
sieves (3 .ANG.) for 24 hours. After this treatment, the IR
spectrum between 1880 and 1450 cm.sup.-1 and the Visible spectrum
between 500 and 700 nm of the solution, having [Nd]=0.33 M, are
measured, under the same conditions and with the same equipment as
examples 2a and 2b, and the results obtained are indicated on the
calibration curves of examples 2a and 2b, providing the following
results: VersH/Nd=0.5 (molar ratio); H.sub.2O/Nd=0.03 (molar
ratio).
Example 5
A cyclohexane solution of Nd(Vers).sub.3, having [Nd]=0.089 M, is
obtained by the preparation of example 1.
The IR spectrum between 1880 and 1450 cm.sup.-1 and the Visible
spectrum between 500 and 700 nm of this solution, are measured,
under the same conditions and with the same equipment as examples
2a and 2b, and the results obtained are indicated on the
calibration curves of examples 2a and 2b, providing the following
results: VersH/Nd=0.011 (molar ratio); H.sub.2O/Nd=1.4 (molar
ratio).
Example 6
Preparation of Anhydrous Nd(Vers).sub.3
(a) 30 ml of the solution of example 5 are transferred to a tailed
Schlenk-tube containing an appropriate quantity of molecular sieves
3 .ANG.. After maintaining the solution under these conditions, at
room temperature for 36 hours, the IR spectrum between 1880 and
1450 cm.sup.-1 and the Visible spectrum between 500 and 700 nm, are
measured, under the same conditions and with the same equipment as
examples 2a and 2b, and the results obtained are indicated on the
calibration curves of examples 2a and 2b, providing the following
results: H.sub.2O/Nd=0.025 (molar ratio).
The process of the present invention allows a solution of
lanthanide carboxylate to be obtained in a simple way, which can be
used as such in the polymerization of dienes, without having to
subject it to vacuum distillation, until the carboxylate is
obtained in solid form, to eliminate the acid and water
impurities.
(b) Alternatively, in order to speed up the operation of the
previous point (a), the solution can be circulated, with a specific
pump, through a cartridge suitably filled with molecular sieves 3
.ANG.. In this way, after 2 hours there is a molar ratio of
H.sub.2O/Nd=0.045, again measured using the calibration curves of
examples 2a and 2b.
Examples 7 to 12
Polymerization of Butadiene
Examples 7 to 12 relate to a series of polymerization tests for the
preparation of polybutadiene with a high content of 1,4-cis-units,
effected using a catalytic system comprising Nd(Vers).sub.3
prepared according to examples 3, 4 and 6, di-iso-butylaluminum
hydride DIBAH and di-iso-butylaluminum chloride DIBAC as
cocatalysts.
The specific polymerization conditions of each example and the
results obtained are indicated in table (I) below, which specifies,
in succession, the reference example number; the Nd(Vers).sub.3
used and the example number in which the preparation is described,
the content of versatic acid expressed as a molar ratio with
respect to the neodymium, the H.sub.2O content expressed as a molar
ratio with respect to the neodymium, the temperature increase of
the reaction mixture observed by operating under adiabatic
conditions, the time used for reaching the maximum temperature, the
butadiene conversion and the time used, the number average
molecular weight (M.sub.n) and the molecular weight value at the
peak of the molecular weight distribution curve of the polymer
produced (M.sub.p).
The polymerization is effected in a 1 liter glass reactor, equipped
with a magnetic entrainment anchor stirrer and external jacket
connected to a heat exchanger for the temperature control. Before
each test, the reactor is previously flushed by washings with
anhydrous cyclohexane (2.times.400 g) at a temperature of
90.degree. C. for at least 2 hours. After discharging the washing
solvent, the reactor is cooled to 25.degree. C. and the following
products are charged in order: 400 g of anhydrous cyclohexane, the
established quantity of di-iso-butylaluminum hydride and
di-iso-butylaluminum chloride, as 0.8 M and 0.9 M solutions in
cyclohexane, respectively, and 42 g of freshly distilled
1,3-butadiene, by passage from two 1 m steel columns filled with
alumina pellets and molecular sieves (3 .ANG.), respectively. The
reactor is then brought to the desired polymerization temperature
(60.degree. C.) and the cyclohexane solution containing the desired
quantity of Nd(Vers).sub.3 is transferred, under a stream of inert
gas, to a metallic container, from which it is introduced into the
reactor by means of an overpressure of nitrogen.
The polymerization reaction is carried out adiabaticcally, by
emptying the reactor jacket as soon as the polymerization reaction
has been triggered. After the period of time established (generally
varying from 30 to 60 minutes), the polymerization reaction is
interrupted by discharging the contents of the reactor, through a
valve situated on the bottom, into a suitable container, containing
800 ml of a 2% by weight solution of Irganox in ethyl alcohol. The
polymer which is separated is left immersed in this solution for 2
hours, it is then recovered and vacuum dried at a reduced pressure
of 1000 Pa, for at least 8 hours, in order to completely eliminate
possible traces of non-reacted monomer and solvent. The solid thus
obtained is weighed and the conversion calculated, finally the
content of 1,4-cis units is measured by means of the known
techniques based on IR spectroscopy and the (M.sub.n) and (M.sub.p)
values are calculated by means of GPC analysis. The results
obtained are indicated in table I below.
TABLE-US-00002 TABLE I polymerization of butadiene according to
examples 7 to 12.sup.(a). Nd(Vers).sub.3 VersH/Nd H.sub.2O/Nd
.DELTA.T t (T.sub.max) Conv. (%) M.sub.n M.sub.p Ex. (ref.ex.)
(mol/mol) (mol/mol) (.degree. C.) (min) t, (min) (.times.10.sup.-3)
(.times.10.sup.-3) 7 3(a) 0.9 1.2 -- -- -- -- -- 8 3(b) 0.012 1.3
27 15 98 in 45' 149 202 9 4 0.5 0.03 29 13 99 in 45' 156 289 10
6(a) 0.011 0.025 34 9 99 in 30' 123 176 11 6(b) 0.011 0.045 31 10
99 in 35' 127 187 12.sup.b 3(a) 0.9 1.2 24 20 98 in 60' 120 181
.sup.(a)Each example was carried out using; cyclohexane (400 g),
butadiene (42 g), Nd(Vers).sub.3 (0.1 mmoles), DIBAH (0.6 mmoles),
DIBAC (0.3 mmoles), by triggering the reaction at 60.degree. C. and
effecting the polymerization under adiabatic conditions. All the
polybutadienes obtained have a content of 1,4-cis units >96.5%
.sup.(b)In this example DIBAH = 1.2 mmoles
As it can be seen from the data summarized in Table I, the use of
Nd(Vers).sub.3 containing the lowest quantity of versatic acid and
water (Ex. 10), allows polybutadiene to be obtained with the lowest
molecular weight (M.sub.n and M.sub.p). Furthermore, the low
versatic acid and water values enable a more rapid reaction
kinetics to be obtained (Ex. 10 and 11), as demonstrated by higher
.DELTA.T values and by the fact that complete conversions are
reached in much shorter times. The presence of greater quantities
of water (Ex. 8) or versatic acid (Ex. 9) causes an increase in the
molecular weights of the polybutadiene obtained and a significant
slowing down of the reaction rate. Finally, the use of
Nd(Vers).sub.3 containing high quantities of versatic acid and
water (Ex. 7) does not allow a polymer to be obtained, under these
conditions. Using the same precursor, it is possible to obtain the
polymer by increasing the quantity of DIBAH in the formulation of
the catalytic system (Ex. 12). In this case, in fact, by doubling
the initial quantity of DIBAH, a polymer is obtained with molecular
weights (M.sub.n and M.sub.p) comparable to those obtained in
example 10, but the polymerization kinetics are much slower: lower
.DELTA.T and complete conversion reached in double the time.
* * * * *